Technical Field of the Invention
The present invention relates, generally, to a flow inducing ring for directing barrier fluid along a desired flow path within a mechanical seal.
More particularly, the present invention relates to a mechanical seal comprising a flow inducing ring with grooves that are preferably of constant, or equal, cross-section throughout their lengths for providing a more uniform fluid flow.
Description of the Prior Art
Mechanical seals are typically used to separate a first fluid from a second fluid. In the context of a pump, for example, a mechanical seal is mounted so as to extend between the pump shaft and the pump housing.
A mechanical seal for separating a first fluid from a second fluid includes a rotary assembly for mounting on a rotatable shaft for rotation therewith and a stationary assembly for securing to a fixed structure within which the rotary assembly is located. Such a seal includes a “floating component” which forms part of either the rotary or the stationary assembly and which is axially moveable relative to the rotatable shaft. In addition, the seal includes a “static” component which forms part of the other of the rotary and stationary assemblies, this component being axially fixed relative to the rotatable shaft. The floating component has a flat angular end face or seal face which is directed toward the static component, usually by means of one or more springs, to close the seal faces together to form a sliding face seal.
A seal with a floating component forming part of the rotary assembly is described as a rotary seal and a seal whose floating component forms part of the stationary assembly is referred to as a stationary seal.
If the sliding seal between the rotary and stationary components is assembled and pre-set prior to despatch from the manufacturer, the seal is referred to as a “cartridge seal”. If the rotary and stationary components are despatched in unassembled form from the manufacturer, the seal is a “component seal”.
A mechanical seal may be single mechanical seal or a multiple mechanical seal, typically a double or triple mechanical seal. Furthermore a mechanical seal may include a barrier fluid system by means of which a third fluid, normally a liquid, is fed to the seal and this third or barrier fluid acts to separate the first and second fluids and is intended to facilitate the removal of heat generated between the sliding seal faces, thereby helping to prolong the life of the seal.
In order for the barrier fluid system to be effective, the barrier fluid has to be fed to the seal and, within the seal, to one or more areas where cooling is to be effected and thence is fed away from the seal. This involves axial movement of the barrier fluid and to some extent this is adversely affected by the forces induced as a result of the rotation of the rotary assembly relative to the stationary assembly.
Previously, a flow inducing ring has been used to direct barrier fluid within a mechanical seal. Furthermore, the deleterious effects of rotation on the axial movement of the barrier fluid have been overcome by using a flow inducing ring 113 as described in United Kingdom Patent Application No. 2,347,180 and depicted in FIGS. 3 and 4 thereof. The flow inducing ring 113 is located within the mechanical seal and is mounted to rotate with the shaft. FIG. 3 indicates the flow inducing ring comprises at least one groove 115 extending both axially and circumferentially in one direction across the ring and at least one other groove 116 extending both axially and circumferentially in the opposite direction across the ring. Grooves extending in the same direction are configured to form “single grooves” 1137, whereas grooves extending in opposite directions and converging on the inboard or outboard edge of the body portion 1131 form “double grooves” 1138. An example of a resulting pattern of grooves is shown in FIG. 4 and comprises alternating double and single grooves. The grooves are arranged such that barrier fluid is caused to flow in the same direction regardless of the direction of the rotation of the shaft. In the flow inducing ring depicted in FIGS. 3 and 4, the grooves are arranged to always propel barrier fluid from the inboard side towards the outboard side of the flow inducing ring, i.e. in the outboard direction. When the shaft and thereby flow inducing ring is rotated in a first direction, grooves 115 are effective to cause the barrier fluid to flow from the inboard side of the ring to the outboard side of the ring in the outboard direction. Then, when the shaft (and flow inducing ring) rotates in the second and opposite direction, grooves 116 are effective to cause barrier fluid flow in the same outboard direction (from the inboard side to the outboard side of the ring). Accordingly, the barrier fluid is directed to flow in a particular direction irrespective of the direction of rotation of the flow inducing ring and shaft.
Unfortunately, there is a significant problem with this particular design. It has been found that barrier fluid is not only directed in the desired barrier fluid flow direction when the flow inducing ring is rotated. More specifically, it has been found that barrier fluid is also drawn into and directed along the grooves in the opposite direction to the desired flow path whilst the flow inducing ring is rotating. For example, whilst the fluid inducing ring rotates in the first direction and grooves 115 act to propel barrier fluid in the outboard direction, barrier fluid is also drawn into grooves 116 and directed along these grooves in an inboard direction from the outboard side towards the inboard side of the ring. Likewise, when the fluid inducing ring rotates in the second and opposite direction and grooves 116 act to propel barrier fluid in the outboard direction, barrier fluid is also drawn into grooves 115 from the outboard side of the ring and directed along these grooves in the inboard direction to the inboard side of the ring.